Assuming your measurements and btu/h's are correct, 1-1/4" will do it with a little room to spare. You can't downsize to 1" though.

I didn't make it clear that you need 1-1/4" gas service to do this, so you may need to reconfigure the existing pipe in the house a little bit if the main line isn't 1-1/4". After all, you're going to be pulling a lot more gas through it, and anything smaller than 1-1/4" will be too small. I'm oversimplifying a pretty complicated process, mainly because I can only size pipes if I'm looking at them or a dimensioned plumbing riser diagram. There are ways to downsize the main line as high-demand appliances branch off. Each pipe in the entire system needs to be sized properly, including the pipes to the new tankless units.

Be sure that your inspector will be sizing the pipe based on IRC/IPC International codes, and not another model code. Most of the nation uses the International codes, but not all do...And pipe sizing methods vary between codes.

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Isn't black iron more expensive than galvanized? We're allowed to use galvanized here for gas as well as long as it's above ground. Actually cannot use black OR galvanized underground unless it's wrapped, otherwise have to use coated pipe.

I don't think there's much of a price difference, but I haven't bought any lately. Galvanized can be used by code as far as I can tell, but it is never done that way here. Never. Alan, since you're in California you probably see more galvanized gasline because of the corrosive environment. Closer to the ocean, black pipe wouldn't hold up all that well I bet. Underground we use plastic about 99% of the time.

Assuming your measurements and btu/h's are correct, 1-1/4" will do it with a little room to spare. You can't downsize to 1" though.

I didn't make it clear that you need 1-1/4" gas service to do this, so you may need to reconfigure the existing pipe in the house a little bit if the main line isn't 1-1/4". After all, you're going to be pulling a lot more gas through it, and anything smaller than 1-1/4" will be too small. I'm oversimplifying a pretty complicated process, mainly because I can only size pipes if I'm looking at them or a dimensioned plumbing riser diagram. There are ways to downsize the main line as high-demand appliances branch off. Each pipe in the entire system needs to be sized properly, including the pipes to the new tankless units.

Be sure that your inspector will be sizing the pipe based on IRC/IPC International codes, and not another model code. Most of the nation uses the International codes, but not all do...And pipe sizing methods vary between codes.

Believe me I'm following you I'm running this 1-1/4" main from the meter, there is a 1-1/4" fitting there now that runs a copper pipe about 40 feet to the fireplace the pipe is tiny looks like .5 inches. I think the meter will accept a bigger fitting that I may be able to connect a 1-1/2" pipe to, I will check and get back, I will also take some pics, perhaps you can take a look if you have a second to spare and comment.

That 40' copper pipe sounds to me like it is your longest run of pipe, so you need to base the sizing off it. Sounds goofy because it doesn't have anything to do with the new work, but that's how gaslines are sized these days.

With 40' longest run and 700000 btu/h's, your 1-1/4" pipe will be undersized. 1-1/2" will be needed. Once you've dropped 40,000 btu/h's off the main line (tees to other appliances), you can bump it down to 1-1/4".

But, like we talked about...Call the inspector first. Better to ask first than to beg for forgiveness later!

I'll check back, but I'm off to the lake for the weekend, so perhaps one of the plumbers that frequent the site can pick up.